can you change the server port from 51820 to one low port, e.g. 1080 etc.?

Also when you use this, do not connect to the router which is the server at the same time, use your carrier data and try.

When you are connect to the Wireguard server’s wifi and want to connect to the Wireguard sever at the same time, it may not work. Of course it does not make sense because you are in its direct wifi network.

So when you set up a Wireguard server, alway turn off your phone’s wifi and use your carrier data to test. This is what you will do when you travel.